GH-48591: [C++] Use C++20 standard functions in bit_util.h

[imraniac]

Rationale for this change

This change replaces custom implementations of bit manipulation functions with C++20 standard library functions from the header. This will reduce the code complexity.

What changes are included in this PR?

Updated the cpp/src/arrow/util/bit_util.h file to replace the custom implementation for PopCount, CountLeadingZeros, and CountTrailingZeros with C++20 standard library functions std::popcount(), std::countl_zero() and std::countr_zero() respectively.

Are these changes tested?

Yes

Are there any user-facing changes?

No, this is an internal refactoring of bit utility functions.

• GitHub Issue: [C++] C++20: use standard bit utils #48591

[github-actions]

⚠️ GitHub issue #48591 has been automatically assigned in GitHub to PR creator.

[pitrou]

Thanks for the PR @imraniac . This is fine, but I think in general we can simplify a bit further. Two suggestions:

1. PopCount, CountLeadingZeros and CountTrailingZeros are now trivial wrappers around std functions, so how about we remove those wrappers and call the std functions directly?

2. NumRequiredBits can similarly be replaced with std::bit_width, can you do this as well?

[pitrou]

cc @zanmato1984 FYI

[pitrou]

This PR is obsoleted by #49298, closing.